Bellows of various types are used in a wide variety of industrial machines and products. Bellows which have a closed cross section are used for such applications as protecting shock absorbers, lead screws, hydraulic rods, and various other machine parts from contaminants, and for conveying or pumping gases or fluids. Bellows which have an open cross section are commonly used for protecting linear ways in machine tools and similar components of industrial machinery. Prior art bellow designs can be classified into three categories: the folded bellow, which is made by forming discrete fold lines into a tube or sheet of foldable material; the corrugated bellow, which is made by permanently stretching the material significantly to form an undulating surface onto a tube or a sheet; and the layered bellow, which is made by selectively bonding the edges of a stack of sheets.
Folded bellow designs, to which the present invention specifically relates, are used widely in industry because they have a high extended length to compressed length ratio, and they are relatively easy to custom fabricate. Prior art fold patterns which are used for folded bellows by companies today are very traditional and have been used for centuries. A useful reference which shows the two main traditional prior art fold patterns is "Materials for Bellows Type Protective Devices" by E. A. Annenberg, E. A. Maiorova, I. M. Sokhor, in Machines and Tooling, v 33, n 11, 1962 p. 39-42. In that reference, FIG. 2 and FIG. 3 show two classic fold patterns used for forming the corners of bellows. For the sake of discussion, these fold patterns, which form the corner of a bellow, will be given names. In FIG. 3 of Annenberg et. al, each V-shaped fold pattern, which forms the corner of a bellow, will be referred to as a single inversion. In FIG. 2 of Annenberg et. al, each V-shaped fold pattern that has an additional fold connecting the wings of the V will be referred to as a classic double inversion. Single inversions and classic double inversions are widely used to form the corners of bellows in industry. Also in Annenberg et. al, FIG. 4 shows an unusual double inversion pattern which is particularly used for a hexagonal closed cross section bellow, proposed by the Russian designer Pavchinskii. Since the Pavchinskii design cannot have an arbitrary cross section, it is not used in industry.
A deficiency of single inversions and classic double inversions commonly used in industry are that when they are extended, they impose outward tilting, or inward tilting, respectively, on the bellow walls. To prevent this undesirable wall tilting when the bellow is extended, shape holding frames are used which are sewn in between adjacent folds, and floppy rubberized fabrics are used to allow the fold lines to undergo gross distortions. Using either single inversions or classic double inversions, the design paradigm has been to use shape holding frames to provide the structural rigidity, and floppy rubberized fabrics to allow gross distortions of the bellow fold lines when the bellow is extended. This prior art design paradigm means that an expensive multi-step assembly process must be used to make the bellow and expensive rubberized fabrics must be used for the folded material.
As stated earlier, all major bellow manufacturers which make protective covers use either single inversions or classic double inversions to form the corners of bellows. As a result, bellow manufacturers of today are forced to use the costly design paradigm for bellows discussed earlier. For example, in the Design Handbook provided by Milwaukee Protective Covers--P.E.I., Milwaukee, Wis., several way cover bellows are shown which use a classic double inversion to form the bellow corners. Page 5 of the handbook shows several PVC stiffening panels which are welded between each fold of a special flexible material. In the Product Guide supplied by Protect & Hema, L.L.C., Loves Park, Ill., on page 15 is shown the underside of a bellow that uses a classic double inversion, which has a complex assembly of stiffening panels and straps to prevent the bellow from overextending. These extra parts are needed because the folded material itself is too floppy to give the bellow support. On pages 17 and 18 are shown bellows that use single inversions to form the bellow corners and plastic stiffening panels glued underneath each bellow panel. In another example, a product flyer provided by A&A Mfg. Co., Inc. of New Berlin, WI entitled "Gortite.RTM. Linear Rail Covers" shows several way covers which use classic double inversions to form the bellow corners with stiffening panels at each fold. Another manufacturer, Centryco.RTM. of Burlington N.J., in their flyer entitled "Centryco Bellows Selection & Design Guide" shows some closed cross section bellows which use classic double inversions to form the bellow corners with stiffening panels sewn in at each fold.
Another relevant area of prior art is passage protection devices for articulated buses or trains. In U.S. Pat. No. 5,471,934, a novel tongue and groove fold is shown to form the corner of a bellow which can provide long extension lengths. While the geometry of this fold is different than either the single inversion or the classic double inversion, it still requires a flexible fabric to be used, and stiffening frames to be attached on either side of the fold. Therefore, this fold does not change the design paradigm described for bellows and hence is costly and complex.